Well. Wow. I can honestly say I've never been anywhere like Harrow before. Especially not a school. It was...grand.
We were shown around by a master, and saw loads of classrooms, dining rooms, boarding houses, sports halls - you name it.
I was mainly there, it seems, as Sherlock's trusty steed. Well, there's a massive advantage to having him on my shoulders - it's far harder for him to run off! Although now I have to hold onto his ankles all the time. He's developed a system of dismount otherwise, which involves (with no warning) unhooking his legs from my shoulders, grabbing my collar/shirt and sliding down my back very fast. Resulting in me being strangled and him escaping. And to think it wasn't long ago when he'd only sit up there if John held his hand.
Mycroft and his mum asked a lot of questions. John asked some questions. I tried to stop Sherlock asking questions, and not look like a fish, with my mouth hanging open all the time. Or laugh as Sherlock tried to wriggle free of John's grip in the science labs. He was like an eel on a line, twisting and turning and struggling, and John was just standing, calm as you like, completely focussed on what was being said as his arm was almost removed.
I did almost spit coffee across the room when fees were discussed, though...
So, obviously it's up to Mycroft if he wants to tell you his impressions, but they got as far as starting to discuss which house he might join...which I assume is a good sign?