The city’s public schools were open for business yesterday — but apparently, somebody forgot to tell the kids.

More than half a million students played hooky in the wake of the storm, yielding one of the lowest school-attendance rates in recent memory — 46 percent.

The figure included nearly 90 schools — mostly high schools — where more than 75 percent of students were absent, according to city data. A number of schools also reported low teacher turnout.