in my 55 i have 10 various cories, including one peppered. i wouldn't say they all school together, but the different species do tend to hang out with each other the most - the two albinos are always near each other, the 4 bronzes do their 'huddle' all the time, the one emerald hangs out with the bronzes, the two barbatus are very independent of each other and the rest of the cories, but do swim near them, and the lone peppered just likes to visit with everybody.
i'd pick up some more cories for your lonely peppered, even if they are a different species.