My slender son used this when he was in 6th grade through 7th grade. The size label has faded, so I'm sorry, I can't tell you the exact size. My current 8th-grade son wears a size 26 swimsuit, and this is one size smaller than that. There's some pilling on the seat, but it's still perfectly usable. My son is slender and tall. He used this during the period mentioned above. It might fit a normally proportioned 5th-grade boy just right, or perhaps a little big. Instant purchase OK! (^o^)