Safe Teachers Assistance and Return To School Act of 2021 or the STARTS Act of 2021 This bill allows an increase in the tax deduction for the expenses of elementary and secondary school teachers in 2020 or 2021 for the purchase of personal protective equipment during the COVID-19 (i.e., coronavirus disease 2019) national health emergency. Specifically, the amount of the deduction is increased from $250 to $1,000, and $750 of such increase may only be used to purchase personal protective equipment or cleaning supplies to combat the spread of COVID-19. Any unused deduction amount for taxable year 2020 may be carried over to taxable year 2021.