Pros
Good salary and benefits. Some divisions have wonderful cultures, others do not. It is such a large company that it really depends on your division. I worked with some absolutely wonderful people and also with (and for) some sadistic ones. The most petty, crazy, evil people I have ever known were managers there, and upper management did nothing about that, in spite of documented complaints.
Cons
The company is too large. Its mission to promote learning gets lost in profit-making. Decision-makers are not educators, yet they design educational products. Pearson acquires companies to make them become each other's customers. We were always caught in a budget squeeze. Although the company promotes a worker-friendly environment by sponsoring picnics and contests, our department did not have time to participate because we were frantically busy, trying to do more with less.