つめる of 見つめる comes from 詰める which literally means 'load stuff into' and used as 思いつめる 仕事詰めの毎日 to indicate to do something with much care and great attention; so, direct translation here will be 'stare at'; but all the students, although they may all have her image in mind, would never stare at her simultaneously. Therefore graysesame's "pay special attention to" shows, I suppose, a perfect understanding.
I agree that “stare at” wouldn’t work here. A female student is a rarity in that school and the boys can’t help being conscious of her presence. It’s not that the boys do something for her in particular, but that they just can’t get their eyes off her.