IPtables blacklist- should it be inserted at the TOP of the INPUT chain?

I have been annoyed by the U of Mich grad students poking at my router. So I added a couple drop rules to iptables (with script firewall-start) like so-

iptables -A INPUT -i br0 -s 141.212.121.0/24 -j DROP
iptables -A INPUT -i br0 -s 141.212.122.0/24 -j DROP

This did not work. I think this is because I am incorrectly using iptables. Blacklist rules need to go at the top, am I correct? Or else they will be let through by the same rule that let them in before and your nifty blacklist...

IPtables blacklist- should it be inserted at the TOP of the INPUT chain?