classroom, they are just not powerful enough and they certainly do not seem to provide the output the spec suggests.
I find the best speakers for classrooms are the Pulse 30w active or 50w active from CPC Farnell - they are about £40 to £50 a pair and come with brackets and some cable.
For non active speakers, the best option is Vision's SP-1300 and these are a good buy from Misco.