We have had several school changes with a kid who gets anxious about change and loves routine and predictability. We also did what Chay suggested - made a list of cons of the old school from what DS had complained about all year long and a list of "pros" that he would gain by switching schools. We included impacts on free time, commute, extra curricular activities, lunch offerings at school, PE activities offered, field trips etc in our list.
Then, we assured DS that it was just a meeting and not a commitment and took him to talk to the administrator in the new school and asked all our questions in an atmosphere of "no pressure". DS is usually present and observes these meetings. We asked to see what books they used for literature reading, what their educational philosophy is, what the math curriculum looked like, what the computer classes were like etc. Then, we had DS visit the classroom and had the teacher talk to him. At that point, when he saw that the class had kids just like him and to them, being in that school was their "normal", DS agreed to shadow the class. We make it clear that after the shadow day, he gets to make the final decision.
He usually likes the new school after the shadow day because he already knows the "pros" of switching from our discussions and he also feels comfortable in the new environment after the shadow day.
The changes were always rough with anxiety making DS sleepless and the stress making him irritable. He also gets forgetful during periods of stress and loses a lot of his belongings, so I have to be extra alert about them. It is an upheaval to both him and us. The last school switch came at age 8 and maybe because of his greater awareness, he feels the effects of the switch more than before. But, he says that he is very happy that he changed schools and that I should have "forced" the issue a lot earlier than listening to him!