In episode 3 of The Queen's Gambit, Beth and her adoptive mother travel the country to compete in many chess tournaments. During their travels, Beth is acquiring more and more fame all the while she is absent from her high school classes.
In one montage, we see that Beth's adoptive mother contacts the high school numerous times to call her daughter in sick with a severe cold or even a bad case of the flu.
How could the school possibly keep believing all these calls while Beth had basically become a national chess hero in the meantime? They would most certainly have known if one of their students attained such status?