[squid-users] Squid will not connect from outside

I am having problems connecting to Squid from outside my local
network. I have set it up using NCSA authentication, and all seems
correct. I can connect to it from within my local network (I commented
out the 'http_access allow localnet' in squid.conf for that test) and
it correctly asks for username and password and connects if right. I
can do this both by referring to my computer's hostname within the
local network and by referring to my router's IP address (I have set
up port forwarding for port 3128 on my router). However, when I try
from outside my local network (from at school), Firefox (using
FoxyProxy) shows a 'proxy server refusing connections' error. This
occurs both when I try to connect via the proxy server and when I nc
into 3128 on my router's IP. Other services (such as ssh) work from
school to my computer at home. Does anyone know why this might be?
Thanks for any help.

--
Tom Dickson-Hunt