This stock flow model uses three years of behaviour data from the school's own management system (Years 7 to 9) to analyse how debits, achievements, and detentions accumulate over time, and to project that pattern into Years 10 and 11.
Three stocks are modelled: Debit Stock, Achievement Stock, and Detention Stock. Monthly inflow rates are calculated from real school data using 10 months per academic year. All outflows are set to zero, reflecting the observable fact that the school's current policy contains no mechanism for clearing or resetting accumulated debits or detentions.
The model is validated against real data to within 0.5% accuracy. Baseline starting values are: 474 debits, 381 achievements, 223 detentions (March 2026).
Three scenarios are tested. Current practice: detention stock reaches 525 by end of Year 11. 4:1 intervention (Teacher_Adaptation 0.8): detention stock reaches 340. Maximum intervention (Teacher_Adaptation 1.0): detention stock reaches 277. All three scenarios produce continued accumulation because the structural outflow remains zero.
Key finding: without a policy mechanism that clears accumulated burden, no level of improved teaching practice alters the mathematical outcome. This demonstrates a policy-resistant system in Meadows' terms. For a pupil with a confirmed ADHD diagnosis, an accumulation-only policy produces unequal outcomes by design.
Data source: school behaviour management system, March 2026.
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