I was shunted around a lot between the ages of 5 and 16. I went to 4 different Primaries, and 4 different Secondaries. I was always the 'new girl'.
Some ages were easier to move than others.
I moved in Reception, and don't even really remember the first school.
I moved in Y3, and that was fine, made friends very quickly.
Moved at the end of Y5, started Y6 in a new school. THAT was a hard move, nobody saw the point in making friends with someone for just one year, when they might not see me at Secondary.
Started Secondary with quite a few from that Primary school - and they became my best friends!
Moved at the end of Y8, started Y9 in a new school. Had no trouble making new friends.
Moved at the start of Y11, again, an unmitigated disaster. Again, nobody saw the point in making an effort with me as they already had their friendship groups, and were leaving in less than a year.
Moved again, but to a different school system in Scotland, and was moved down a year and put in what was Y10. Had no trouble making friends.
My advice? Don't move for the start of Y6 or Y11, it will be miserable for your child.
If your child is younger, give it AT LEAST a term for them to settle and break established friendship groups.
HTH.