Developmental, cognitive and behavioural assessment tools — formative SAQs

SAQ 1 — Surveillance, screening and diagnosis: three acts, one schedule (15 marks, 15 minutes)

A registrar asks you to explain how developmental, cognitive and behavioural assessment fits together, from the routine well-child visit to a confirmed diagnosis. ^[1]

Question. Distinguish developmental surveillance from screening and from diagnostic assessment, state the recommended screening schedule, and name the correct tool for a broadband developmental concern, an autism concern and a diagnostic cognitive assessment. Explain the standard-score model and why a positive screen is never a diagnosis.

Model answer

Three acts (4 marks). Surveillance is the longitudinal, opinion-based monitoring performed at every health visit, drawing on history, examination, observation and parental concern. Screening is a brief, standardised tool applied to the whole population at scheduled ages to find the child who needs a closer look. Diagnostic assessment is the lengthy, trained-administered evaluation that confirms and quantifies a disorder. A screen can never do the diagnostic tool's job. ^[1]

Schedule (3 marks). Developmental surveillance at every visit, layered with a standardised developmental screen at nine, 18 and 30 months and an autism-specific screen (M-CHAT-R/F) at 18 and 24 months. The scheduled screen reaches the children no one is yet worried about. ^[1]

The right tool (4 marks). For a broadband developmental concern, a parent-completed screen such as the Ages and Stages Questionnaires (one to 66 months, five domains) or PEDS (nought to eight years, ten concerns). For an autism concern, the M-CHAT-R/F (16 to 30 months). For a diagnostic cognitive assessment, refer for the Bayley Scales up to 42 months, or the Griffiths or Wechsler scales for the older child. A 2024 meta-analysis used Bayley as the reference standard against which the parent-completed screens were compared, confirming that screens do not substitute for diagnostic assessment. ^{[3] [9]}

Standard-score model and the meaning of a screen (4 marks). A standard cognitive score has a mean of 100 and a standard deviation of 15, so a score of 70 or below sits two standard deviations below the mean and marks significant concern. Because developmental disability is common but population prevalence is low, a screen's positive predictive value is modest, so a positive screen is a reason to refer, never a diagnosis. ^{[9] [10]}