No matter what school you go to, the gym clothes are all just spats and half-pants.
Literal
Which school [even-であっても], gym-clothes [topic-は], spats [and-や] half-pants [only-ばかり] [copula-だ].
であっても ('even if it is / no matter which') is the formal concessive form of the copula. 体操着 (たいそうぎ, 'gym clothes') is the standard school term. スパッツ ('spats/leggings') and ハーフパンツ ('half pants/shorts') are loanwords for modern athletic wear. ばかり ('nothing but / only') expresses a complaint about uniformity. The speaker is lamenting the lack of variety across schools — every school uses the same boring options.