The number of primary test cheating cases has soared by more than 50 per cent in two years.

The Standards and Testing Agency (STA) carried out 793 maladministration investigations across key stage 1 and key stage 2 in 2018, up from 524 in 2016, new figures show.

Related: 1,500 Sats results investigated for potential cheating

Background: Huge rise in Sats cheating probes

Maladministration: Almost 600 primaries investigated for cheating

A majority of the 2018 investigations (644) involved KS2 tests. Of these, 623 related to the tests themselves and 21 related to teacher assessment.

Sats cheating

The remaining 149 STA investigations involved assessments at KS1. Of these, 62 related to the phonics screening check, 66 related to KS1 tests and 21 related to teacher assessment.

The proportion of cases resulting in an amendment or annulment of results has also risen.

At KS1, the percentage of all cases amended or annulled has risen sharply from 2.1 per cent in 2016 to 14 per cent in 2018.

At KS2, the proportion increased from 15.1 per cent in 2016 to 15.8 per cent in 2018.