I think it's clear by now that you're confusing "teaching about Islam, in the context of studying world religions" and "teaching Islam", as in endorsing, promoting, and coercing students into converting, as the school in the OP did with Christianity.
having students recite Islamic prayers I would call proselytizing ..
how is posting the 5 pillars of Islam different then posting the 10 commandments ???
I also don't think teaching the tenants of ANY religion is proper in a k-12 school ..
in a university I have no problem with ..