School chromebook bandwidth problem

Hi there - we are a small school and have recently purchased 30 chromebooks. We have a wifi network with access points in each classroom. We also have a suite of laptops that happily all connect to the internet at the same time. With the chromebooks, as soon as more than 6 or 7 are turned on, the bandwidth collapses - I have tested it using iplayer and streaming radio but it ends up saying you are not connected to the internet or not enough bandwidth. I have spoken to a few people and they commented that there are certain tweaks for classroom chromebooks - I just can't seem to find them! Any help gratefully received