This is the 17534th most frequent Russian word.
требовательные
Demanding.
In this sentence, 'требовательным' describes the nature of the teacher's expectations toward their students, emphasizing strictness and high standards.
Учитель был очень требовательным к своим ученикам.
The teacher was very demanding of their students.
Here, 'требовательными' refers to the parents' insistence on proper fulfillment of responsibilities in a home setting.
Родители оказались требовательными к выполнению домашних обязанностей.
The parents turned out to be demanding regarding the completion of household chores.
In this context, 'требовательная' characterizes the job as requiring effort and precision from the person performing it.