Discipling Disciples does not work, because you can't gain cards that aren't in the supply.
I find that Teacher is best on boards with easy "spam" targets. If all of your cards are reserves such as transmogrify or Guide, it becomes much less profitable to add tokens, because you will only use the on-play effect every other turn at best. Durations pose a similar issue. Cheaper cards and cantrips are generally much more powerful, especially if you have ample +buy to acquire more copies of the card in question upon Teacher's arrival.
You seldom need a 2nd copy of Teacher; one is usually enough to get out the tokens you need, as often a simple +card or +action token will grant you an extraordinary advantage. However, I do recommend multiple Peasants if the opportunity strikes. Disciple is an outstanding card in engines, and barring the rarest of boards, you CAN build an engine if Teacher is present. Surprisingly, Soldier works well as a payload in the late game if the board contains a large number of attacks. A recent IRL game of mine ended in a megaturn where I made nearly $40 from soldiers alone. Often, this will be redundant, because an engine enabled by Teacher is often strong enough not to need the minor detour for extra coin, but it's a useful trick to keep in mind.
I have yet to find a kingdom where Peasant did not prove worthwhile. I enjoy it more and more the further I play with it, and look forward to whatever new things the forum discovers about it over time.