さえ？

[Half-n-Half]

I came across this sentence when I was studying:

アメリカでは大学生ばかりか、中学生、高校生さえ日本 語を勉強している。

I understand it means "In America not only college students but even middle schoolers and high schoolers are studying Japanese."

What I can't understand is what さえ is doing that も couldn't. Is there some hidden nuance さえ conveys that も doesn't? Thanks for the help.

 

[Toritoribe]

roughly,

～ばかり/だけでなく…も: not only~ but also...

～ばかり/だけでなく…（で）さえ（も）: not only~ but even...