School supplies are cheapest during a window of a few weeks and noticeably dearer outside it. The pattern follows from how concentrated demand for the category is.
A year of sales in a month
Demand for basic stationery, uniform items and school bags collapses into a short period around the start of term.
Sales outside that window are a fraction of the total, so the retailer's whole year in the category is decided by performance during a few weeks.
That concentration makes the period fiercely competitive, because losing a customer means losing them for a year rather than for a week.
Basic items as traffic drivers
Simple, comparable products are the ones shoppers use to judge whether a shop is cheap, because everyone knows roughly what a pack of pens should cost.
Retailers therefore price those items very low, sometimes below cost, to establish the impression that the whole aisle is inexpensive.
The margin is recovered on the rest of the basket, where products are less comparable and price expectations are much vaguer.
Why the same items cost more in October
Once the peak passes, the promotional reason for the low price is gone, and prices return to a level that supports normal category margin.
Remaining stock also becomes a storage problem, so some of it is cleared cheaply while the rest is held and repriced upwards for steady-state selling.
Replenishment through the year comes in smaller quantities at worse buying terms, which raises cost as well as price.
Where the specification quietly changes
Promotional stationery is frequently built to the price point rather than being the same product sold cheaply.
Thinner paper, lower page counts, fewer pens in a pack and lighter card are the usual adjustments, and they are legitimate provided the pack states them.
Comparing sheet counts, weights and quantities rather than pack prices is what makes those differences visible, since packaging is designed to look equivalent.
Uniform and the constrained purchase
Where a specific item can only be bought from one supplier, competition does not apply and the price reflects that exclusivity.
Generic equivalents are far cheaper because many retailers can supply them, which is why the same garment costs very different amounts depending on whether a badge is required.
The wider the specification, the more of the purchase moves into the competitive part of the market, and the more the seasonal window matters.