Most of the times, seats are available from Tsuen Wan West or Mei Foo. My son complains at the begining of the school year last year about not getting a seat in the train in the morning but he has grown out of it now.
My boy loves PE & the Modern lang. the most, and Chinese the least so we are trying our best to encourage him to read more Chinese.
I am sure your child will settle in SM well! As the teachers are very caring.
There are one / two SM pupils which are extremely active in the train such as running and jumping around during their jouney way home on the west rail line last school year, and the helpers just let them be. So if your helper takes your child to school by rail it would be wise to remind the helper and your child not to join in as it's very dangerous. One lady told me on the train once that one time the driver had to made an annoucement to ask them to stop.