Say rather that it's not as efficient, since the atmosphere is nowhere near as conductive for electrical signals as physical wiring is.
As for network congestion... a home network will usually top out at 10 devices or less, where a school's network is more likely to have hundreds of connections (depending on how many computer labs there are, how many office computers the staff & educators have, whether they allow students to access the network with their own devices, etc.).
On the other hand, schools tend to have "business-class" service, which means the ISP is going to guarantee a higher Quality of Service (QoS) than for residential customers. Also, the school network's "node" for testing purposes may be a dedicated node installed at or near the site for the school's use, whereas the home provider has his service hooked up to a box with other residential customers -- & sometimes the line technicians aren't always careful about watching the maximum number of customers they tie into those boxes (my in-laws noticed a loose wire at the TImeWarner box along their back fence, & when the tech came out to look at it he found that 10 homes were hooked up to a box that was only supposed to serve 4 homes).
Try using a speed-testing site that will also analyze your QoS, both at home and at school. Also, for home double-check that you test both the Ethernet & Wi-Fi connections.