Could be a RPG as well, shooter probably winged it. It's range is often extended by users by removing the self-destruct mechanism.
Similar attacks have happened before, a tailor's shop was damaged in the previous attack.
The closest elevation near the school is 1.2KM away, that's more than enough for a modified RPG.
If a 122mm was used, I guess the damage would be much more and itd be on the news by now. Plus it's not an easy weapon to conceal and fire. It's thin, but very tall.
Could be the 107mm rocket, used plenty in the region, but then again, the damage doesn't check out.