Steel frame buildings?
Masts operating at reduced power near the school to deal with 'parent paranoia'?
The former is more likely but the latter is not unknown. Masts operate three 'arrays' on antennae with a covergae of c.130 degrees to allow overlap.
Where there has been significant local opposition to a site operators can 'turn the wick down' to get one or more arrays operating at reduced power.
This satisfies the paranoid who fully forget that the phones pressed against their ;little darlings' heads have to operate at higher power to compensate.
However, signal disruption from a steel framework is far more liklely.