In some parts of the world – Australia, for example – separates are more popular than leotards for training.
But in North America they are the exception, not the norm. Crop tops are worn on very hot days in a few Gyms, for the most part.
Chalk Bucket has a thread on this topic right now. Comparing club policies.
Even odder for those in the general public not familiar with Gymnastics training is the tradition in Men’s Gymnastics of training shirtless.
Gymnastics Coaching.com 
I’ve worked at two clubs that didn’t allow boys to take off their shirts. Total pain and more dangerous because shirts get wrapped around the bar or your hand while spotting, and sometimes fall over their heads while upside down. Dumb rule by owners who want the “appearance” of propriety, but have no problems with girls half naked. Also, it makes measuring angles very difficult especially on rings.
LikeLike
Jagwear in Canada has sold them for a while. I remember talking with them way back when about them for my kids.
LikeLike
I like a leotard. I have on more then one occasion grabbed the leotard in the middle to keep a kid from a hard fall. It was all I could get and I’m glad I had that and not there skin. But I agree with no t-shirts. T-shirts are not safe either.
LikeLike
This is interesting. I coach at the club in Dunedin, New Zealand and we have a gym that is too hot in the summer and literally freezing cold in the winter so we accept workout wear that ranges from crop top and shorts in the summer and then leotards, thermal tops, thermal pants, socks and heat packs in the winter. Interesting seeing other club regulations.
LikeLike