targeting of ads based on click throughs?

With the school year beginning, I am getting homework help ads

[hyperstat]

I have an informational site about statistics. In the last few days I've noticed many more ads about homework help and statistics tutoring (there always were a few). Possibly with the beginning of school the click rate on those ads has gone up and Google has adjusted accordingly. Or perhaps the tutors are buying more ads now. Any comments on how quickly Google adjusts based on click throughs?

[1Lit]

Wow, sounds very sophisticated if that is how Adsense serves ads (based on click-through of a particular advertiser from a particular page).

[Jenstar]

I think it is just because of the whole "back to school" season. Those adverisers are doing higher $$ campaigns, they are doing more of them (using more keywords), and there are likely new advertisers starting up campaigns.

If you have seen them in the past, it is more likely that they have upped their bids, or there are more of them.