Q: This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
From the 1950s on, the students were also used for unpaid work at schools, where they cleaned and performed repairs. This practice has continued in the Russian Federation, where up to 21 days of the summer holidays is sometimes set aside for school works. By law, this is only allowed as part of specialized occupational training and with the students' and parents' permission, but those provisions are widely ignored. In 2012 there was an accident near city of Nalchik where a car killed several pupils cleaning up a highway shoulder during their "holiday work" as well as their teacher who was supervising them.
A:
When were students used as workers?