Effect of Visual Illusion on Motor Skills Learning in Boys With Developmental Coordination Disorder: A School-Based Randomized Controlled Trial

ERCT Criteria Breakdown

• Level 1 Criteria

  • C

    Class-level RCT

    • Randomisation was conducted at the school (cluster) level across nine schools, which satisfies the class-level (or stronger) RCT requirement.
    • "It should be noted that the unit of randomization was the school (cluster), not the individual participant."
    • Relevant Quotes: 1) "This was a three-arm, cluster randomized controlled trial conducted in nine accredited public schools, to examine the effect of the Ebbinghaus visual illusion on motor skill learning in DCD children with DCD." (Methods, Study design) 2) "It should be noted that the unit of randomization was the school (cluster), not the individual participant. To account for the cluster-randomized design, we adjusted the sample size calculation using a design effect based on an estimated intraclass correlation coefficient (ICC) of 0.05..." (Methods, Participants) 3) "Randomization was performed by someone outside the research team to avoid bias." (Methods, Participants) 4) "Block Randomization of schools (n = 9; Number of subjects: 75)" (Figure 1, CONSORT diagram) Detailed Analysis: The paper explicitly and repeatedly states that the unit of randomisation was the school, not the individual student or a class within a single school. Nine schools were block-randomised (by an assessor outside the research team) to one of three conditions, and the design effect / ICC adjustment for cluster randomisation was formally incorporated into the sample-size calculation, confirming that the school was treated as the analytic cluster. Under the ERCT standard, school-level randomisation is stronger than class-level randomisation and automatically satisfies the weaker C criterion, since contamination between treatment arms within the same class or school is prevented by assigning whole schools to a single condition. Final: Criterion C is met because randomisation was performed at the school (cluster) level by a party outside the research team, which exceeds the class-level requirement.
  • E

    Exam-based Assessment

    • The outcome measure was a physical throwing-accuracy task (radial error), not a standardised academic exam; no exam-based assessment was used.
    • "Performance accuracy was measured by radial error (distance from target center to the closest side of the beanbag)."
    • Relevant Quotes: 1) "Beanbag throwing performance was operationalized as the mean deviation from the target across 10 trials during the pretest, practice, and retention phases." (Data analysis) 2) "Performance accuracy was measured by radial error (distance from target center to the closest side of the beanbag). ... higher values of radial error (greater distance from the center of the target) indicated lower accuracy and therefore poorer performance." (Results, Throwing accuracy) 3) "Children performing below the 16th percentile for their age were included. ... The MABC-2 was administered by two assessors with master's degrees in physical education and motor behavior, both of whom had completed formal training in the Persian version of the test..." (Methods, Diagnosis of DCD and measures) -- the MABC-2 is used only as an inclusion/screening tool, not as the study's outcome measure. Detailed Analysis: The ERCT E criterion requires that the primary outcome of the study be assessed with a widely recognised, standardised exam-based assessment (e.g. a national curriculum or academic achievement test). In this paper, the primary and only outcome is a physical motor-performance metric (radial error in a beanbag-throwing task), which is a laboratory/clinical motor measure, not an academic exam. The MABC-2, which is a standardised instrument, is used purely as an inclusion/screening tool for diagnosing DCD, not as the outcome measure of learning. No standardised academic exam of any kind was administered to assess the intervention's effect. Final: Criterion E is not met because the study's outcome was measured via a motor-performance task (radial throwing error), not a standardised exam-based assessment.
  • T

    Term Duration

    • Outcomes were measured only 48 hours after the last training session, and the full study (pretest through retention) ran about six weeks, short of a full term.
    • "Motor learning was assessed using a retention task at 48 hours after the last practice session."
    • Relevant Quotes: 1) "This study started from 2021.08.10 till 2021.09.25." (Methods, Study design) 2) "Motor learning was assessed using a retention task at 48 hours after the last practice session." (Abstract) 3) "Before the retention test, participants again drew the target circle without the surrounding circles, followed by a 10-trial retention test (48 hours post training) without visual illusion." (Apparatus and task) Detailed Analysis: The overall study window (pretest, six acquisition blocks, and retention test) spans from 10 August 2021 to 25 September 2021, roughly six weeks in total -- already shorter than a typical academic term (3-4 months). Critically, the primary retention (learning) outcome that the paper's conclusions rest on was collected only 48 hours after the final training session, not at least one term after the intervention began. There is no later follow-up measurement reported anywhere in the paper. Final: Criterion T is not met because the retention outcome was measured 48 hours after training ended, and the entire study period was well under one academic term.
  • D

    Documented Control Group

    • The control group's size, condition (no illusion), and baseline demographic/performance data are clearly documented and compared against the two illusion arms.
    • "Therefore, the groups were comparable at baseline, and the differences observed in the practice and retention phases can be attributed to the intervention."
    • Relevant Quotes: 1) "...nine were selected using a random number table. These schools were randomly assigned to one of three research conditions: perceived larger target, perceived smaller target, and control (without visual illusion)." (Procedure) 2) "As shown in (Table 1), demographic variables including age, height, weight, and IQ, as well as initial performance in the beanbag throwing pretest, were compared across the three groups. The results of the one-way ANOVA indicated no significant differences between the groups in these variables (all p > .05). Therefore, the groups were comparable at baseline..." (Results, Baseline characteristics) 3) Table 1 reports control-group values for Age (8.48, SD 1.39), Weight (37.9, SD 2.50), Height (136.6, SD 4.2), IQ (85.10, SD 2.24) and Pretest (14.93, SD 2.05), alongside the two illusion arms (n = 25 each). (Table 1) 4) "Allocated to control group (n = 25) ... Follow-up 48 hours after the last training session (n = 25) ... Lost to follow-up (n = 0) ... Analysis (n = 25)." (Figure 1, CONSORT diagram) Detailed Analysis: The control group is well-documented: its size (n = 25), its precise condition (beanbag throwing practice with a projected target hole but no surrounding illusion-inducing circles), and its baseline demographic and performance characteristics are all reported in Table 1 and shown to be statistically comparable to the two treatment arms. The CONSORT diagram further documents retention and analysis numbers for the control arm (zero attrition). Final: Criterion D is met because the control group's composition, baseline characteristics, and condition are documented in detail and shown to be comparable to the intervention arms.

• Level 2 Criteria

  • S

    School-level RCT

    • Nine public elementary schools were the unit of random assignment, satisfying the school-level RCT requirement.
    • "It should be noted that the unit of randomization was the school (cluster), not the individual participant."
    • Relevant Quotes: 1) "This study was designed as a cluster randomized controlled trial conducted in nine accredited public elementary schools in Shiraz, Iran. In the first phase, 12 schools were invited, of which 9 schools agreed to participate and were randomly assigned to one of three experimental conditions..." (Methods, Participants) 2) "It should be noted that the unit of randomization was the school (cluster), not the individual participant." (Methods, Participants) 3) "After randomization, all eligible boys with DCD from each school were assigned to the intervention condition corresponding to their school." (Methods, Participants) Detailed Analysis: The study explicitly identifies the school as the unit of randomisation ("school" here corresponds directly to the ERCT definition of the educational institution implementing the intervention). Twelve schools were invited, nine agreed and were block- randomised as whole units to one of three conditions, with all eligible children in a given school receiving that school's assigned condition. This directly matches the S criterion's requirement of randomisation among schools rather than classes or students. Final: Criterion S is met because randomisation was performed at the level of whole schools (nine schools across three conditions).
  • I

    Independent Conduct

    • Only the randomisation sequence was generated externally; the same research/training team designed, delivered, supervised, and assessed the intervention.
    • "Randomization was performed by someone outside the research team to avoid bias."
    • Relevant Quotes: 1) "Randomization was performed by someone outside the research team to avoid bias." (Methods, Participants) 2) "...all training sessions were performed by two trained trainers with a master's degree in motor behavior and physical education. Prior to the study, the trainers attended a training session to fully coordinate how the guidelines were submitted and were under the supervision of a DCD faculty member." (Apparatus and task) 3) "The MABC-2 was administered by two assessors with master's degrees in physical education and motor behavior, both of whom had completed formal training in the Persian version of the test... Their work was supervised by a senior faculty member with expertise in DCD research to ensure reliability and consistency." (Methods, Diagnosis of DCD and measures) Detailed Analysis: The only independence explicitly documented in the paper concerns generation of the randomisation sequence, which is a narrow allocation-concealment safeguard, not full independent conduct of the trial. The trainers who delivered every arm's practice sessions and the assessors who administered the diagnostic/outcome measures were trained, coordinated, and supervised directly by a faculty member from the same research/university team that designed the study (the paper does not name any external evaluation agency separate from the intervention designers). There is no statement that data collection or analysis were carried out by a third party independent of the study's designers, so the criterion requiring independent conduct of the evaluation as a whole is not satisfied. Final: Criterion I is not met because only the randomisation sequence, not the delivery, data collection, or analysis, was handled independently of the research team.
  • Y

    Year Duration

    • The entire intervention and follow-up spanned about six weeks; criterion Y cannot be met because criterion T (term duration) was not met.
    • "This study started from 2021.08.10 till 2021.09.25."
    • Relevant Quotes: 1) "This study started from 2021.08.10 till 2021.09.25." (Methods, Study design) 2) "Motor learning was assessed using a retention task at 48 hours after the last practice session." (Abstract) Detailed Analysis: The whole study, from pretest through the retention test, took place across roughly six weeks (10 August to 25 September 2021), nowhere near the 75% of an academic year (~9-10 months) required by criterion Y. Per the ERCT specification's dependency rule for this criterion, since criterion T (Term Duration) was already found not met, Y is automatically not met as well. Final: Criterion Y is not met, both on its own merits (a roughly six-week study window) and because criterion T was not met.
  • B

    Balanced Control Group

    • All three arms received an identical amount of practice (60 trials over six blocks); only the visual illusion condition, the treatment variable itself, differed between groups.
    • "During the acquisition phase, each group performed 60 trials (6 blocks of 10 trials) with one minute of rest between trials."
    • Relevant Quotes: 1) "Participants threw beanbags from below shoulder on a level artificial-turf indoor green (400 x 55 cm) to a target from a distance of 2 meters... A ceiling-mounted projector displayed the target 'hole' and the surrounding 8 small circles... or 6 large circles... the distance between the center of target and the nearest edge of the beanbag was measured after each trial." (Apparatus and task) 2) "During the acquisition phase, each group performed 60 trials (6 blocks of 10 trials) with one minute of rest between trials." (Apparatus and task) 3) "In addition, the guidelines for launching a beanbag were provided to all participants in a standard and uniform way, and the extra verbal feedback that could affect the results was avoided." (Apparatus and task) 4) "...all training sessions took place during official school hours... to maintain the uniformity and quality of education, all training sessions were performed by two trained trainers..." (Apparatus and task) Detailed Analysis: Applying the criterion B decision procedure: the intervention does not add any extra time, budget, or materials for the illusion arms relative to the control arm -- all three groups (perceived-larger, perceived-smaller, and control) completed the exact same number of trials and blocks, in the same facilities, with the same trainers, the same instructions, and the same absence of extra verbal feedback. The only thing that differs across arms is the visual illusion condition (presence/absence and type of surrounding circles), which is precisely the treatment variable under investigation. Since no group received additional time, budget, or materials beyond the others, resources are inherently balanced; this also fits the case where the differing element is integral to the design being tested. Final: Criterion B is met because all three arms received identical training dose, duration, and resources, differing only in the illusion condition that is the study's treatment variable.

• Level 3 Criteria

  • R

    Reproduced

    • The authors state this is the first study of its kind, and an internet search for independent replications by other research teams found none.
    • "To our knowledge, this is the first study to examine the effect of visual illusion on motor skill in targeting skills in children with DCD."
    • Relevant Quotes: 1) "To our knowledge, this is the first study to examine the effect of visual illusion on motor skill in targeting skills in children with DCD. The effect of visual illusion on performance has been widely considered in the literature on typical participants, but has been limited for DCD." (Discussion) 2) The paper cites related but non-replicating prior work by an overlapping author (Razeghi et al., 2020, 2022) on visual illusion and autism, and by Bahmani et al. (2018) on visual illusion and typically- developing children -- these examine different populations/tasks, not a replication of this specific DCD beanbag-throwing study. Detailed Analysis: The authors explicitly and directly claim novelty for this specific study design and population (visual illusion and beanbag-throwing motor learning in boys with DCD). No independent replication of this precise study, by a different research team in a different context, is referenced in the paper. An internet search (web search for the paper's title and author names, plus targeted searches for replication studies of visual-illusion beanbag-throwing training in children with DCD) surfaced only a related 2024 Scientific Reports study on visual illusion and self-controlled practice in children at risk for DCD using a golf-putting task (Shahbaz et al., 2024), which is a different task and different design, not a replication of this study. No paper independently reproducing this specific school-based, cluster-RCT beanbag-throwing study was found. Given the June 2026 publication date, the window for independent replication to have occurred and been published is also minimal. Final: Criterion R is not met because the study is explicitly presented as the first of its kind, and an internet search found no independent replication.
  • A

    All-subject Exams

    • Only a single motor-performance measure (throwing accuracy) was assessed, and criterion E was not met, so criterion A cannot be met either.
    • "Performance accuracy was measured by radial error (distance from target center to the closest side of the beanbag)."
    • Relevant Quotes: 1) "Beanbag throwing performance was operationalized as the mean deviation from the target across 10 trials during the pretest, practice, and retention phases." (Data analysis) 2) "In addition, we did not perform a transfer test to evaluate the broader effects of the practice conditions." (Limitations) Detailed Analysis: The study measured a single, narrow motor outcome (beanbag-throwing radial error) and explicitly notes in its limitations that no transfer test to other skills or domains was conducted. There is no assessment of any academic subject at all, let alone all main subjects. Furthermore, per the ERCT specification, criterion A requires criterion E to be met as a prerequisite, and E was found not met since no standardised exam-based assessment was used. Final: Criterion A is not met, both because only one narrow motor-skill outcome was measured and because its prerequisite, criterion E, was not met.
  • G

    Graduation Tracking

    • Follow-up stopped 48 hours after training with no further tracking, criterion Y was not met, and an internet search found no follow-up publication by the same authors tracking this cohort.
    • "Follow-up 48 hours after the last training session (n=25) ... Lost to follow-up (n=0) ... Analysis (n=25)."
    • Relevant Quotes: 1) "Follow-up 48 hours after the last training session (n=25) ... Lost to follow-up (n=0) ... Analysis (n=25)." (Figure 1, CONSORT diagram) 2) There is no mention anywhere in the paper of any longer-term follow-up, later cohort tracking, or planned/published follow-up study beyond the 48-hour retention test. Detailed Analysis: The paper's data collection ends with a single retention test 48 hours after the final training session; there is no tracking of participants into later school years or toward graduation, and no reference to a planned or existing follow-up publication. An internet search for subsequent papers by the same author team (Zamani, Hashemi, Razeghi, Abedanzadeh, Marchant) tracking this same cohort of 75 boys with DCD from these nine Shiraz schools did not find any such follow-up or graduation-tracking publication. Per the ERCT specification's dependency rule, since criterion Y (Year Duration) was not met, criterion G is automatically not met as well. Final: Criterion G is not met because tracking ended 48 hours after the intervention, no follow-up publication tracking this cohort was found via internet search, and because criterion Y was not met.
  • P

    Pre-Registered

    • No pre-registration of the study protocol, registry name, ID, or date is mentioned in the paper, and an internet search of trial registries found no matching registration.
    • Relevant Quotes: No quotes are available: a full-text search of the paper (including Methods, Disclosure statement, Funding, Institutional review board statement, and Informed consent statement) found no mention of a trial registry (e.g., IRCT, ClinicalTrials.gov), a pre-registration platform, or a pre-analysis plan. The only procedural approval mentioned is: "The study was conducted in accordance with the Declaration of Helsinki, and approved by the Kharazmi University Review Board." (Institutional review board statement) -- this is ethics approval, not protocol pre-registration. Detailed Analysis: Ethics board approval documents that the study was reviewed for ethical conduct, but it is not equivalent to pre-registration of hypotheses, methods, and planned analyses on a public registry before data collection began. No such registration is referenced anywhere in the manuscript. An internet search for a matching Iranian Registry of Clinical Trials (IRCT) entry or other registry record for this study (by title keywords and author names) did not locate any pre-registration record for this specific trial. Final: Criterion P is not met because no pre-registration statement, registry ID, or registration date is provided anywhere in the paper, and none was located via internet search.