About the closest any research has come to supporting the tiredness theory is to confirm that adults yawn more often on weekdays than at weekends, and that school children yawn more frequently in their first year at primary school than they do in kindergarten.
关于疲倦论的研究中，最接近于支持它的一个研究也只不过是证实了
成年人工作日比周末更经常打呵欠，
以及
上学的孩子小学一年级时比幼儿园里更经常打哈欠。
（研究证实的现象并不构成对理论很强的支持，承接原文上一句。）
About the closest … has come to doing sth… 是固定结构。
The photo above is the closest humanity has ever come to creating Medusa.
What’s the closest the world has come to actually ending?
ladynbird老师解答VIP学生Tara