The NUT teachers union has paved the way for a potential boycott of Sats in 2018.
At the union's annual conference in Cardiff, delegates voted to "ballot leadership members, in sufficient time to ensure a boycott of Sats in 2018" if the government did not overhaul the current primary assessment regime.
The union will also assess whether there is "sufficient support" among primary members to ballot them for a boycott.
The move follows a similar vote at the ATL's annual conference earlier this week, where 96 per cent of delegates backed a motion to "explore a possible boycott of all tests at primary level".
Samantha Rodgers, a delegate from Rhondda Cynon Taf, led delegates in a chant denoucing primary testing:
Jessica Edwards, a member of the NUT's executive, said testing was "damaging children - it's damaging their education, it's damaging their self-esteem".
"Sats are the head of the monster - let's decapitate it," she said.
Michael Holland, from Lambeth, said teachers "talk about Sats in the way that characters in the Lord of the Rings talk about Sauron and Mordor".
"Let's throw Sats into the Crack of Doom," he added.
And Jane Baker from Lewisham said the current primary testing regime "amounts to a form of institutionalised child abuse".
The threats of action from the NUT and ATL come despite the government mooting the possibility of scrapping key stage 1 Sats last month.
The government has launched a consultation which suggests ending tests for 6 and 7-year-olds and introducing a new "teacher-mediated" baseline assessment to measure school progress.
Kevin Courtney, the NUT's general secretary, told journalists that whether the NUT followed through with a full boycott ballot "depends on how the governent reacts to the consultation".
The vote follows a decision by NUT delegates yesterday to back a one-day regional strike in the summer term over school funding cuts, and tomorrow delegates will vote on a motion to ballot members "on a boycott of all summative testing within primary schools".