The quickest way to learn a new language is through immersion.
This principal was trying to help the Hispanic kids learn English. Not to disparage Spanish in any way.
I have known Hispanic immigrant families who did the same thing at home. One young lady told me her dad would ream into them if he heard Spanish being spoken in the home.
Here in Atlanta my friend’s dad would rail her if she picked up ebonics.
His favorite saying was “there IS an R in four and is NOT one in idea.” Haha