January 19, 2015 2:01 PM EST

Students and teachers returned to a Nairobi-area school from a break to find that a barrier had been erected around their play area by a private developer in an apparent sale of the land.

The Nairobi city council has not commented on the legality of the sale of the land it says is public, the BBC reports, though some protesters allege it was an unlawful land grab. Around 100 students, mostly between the ages of 8-13, along with teachers and activists, knocked over the wall and were met by about 40 armed police officers, some of whom fired tear gas canisters at the demonstrators, the Telegraph reports. At least five children received medical attention.

Write to Nolan Feeney at nolan.feeney@time.com.

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