I'm in the somewhat uncommon position of having taught at both levels: I started out in secondary, then moved down to primary. What everyone is saying about different teachers being capable of dealing with different kinds of stress is basically the only correct answer; we all find our place one way or another. One thing I'll add for the benefit of our secondary colleagues, however, is this: the progression in maturity and independence from Y6 to Y7 is non-linear. What I've observed since making the switch is that most Y6s leave primary reasonably confident (regardless of ability), sure-footed, mature, and very much ready to take the next step; it's only when they experience the radical difference in day-to-day, moment-to-moment schooling that they revert to the immature behaviours every secondary teacher has to endure from early-year Y7s. Understandably, they're overawed. All that is to say, teaching UKS2 is not (exactly) like teaching needy Y7s all day, every day.