Concern is growing about the marking of the key stage 2 writing test this year, as papers are returned to schools.
Steve Iredale, vice-president of heads' union the NAHT, said: "In one morning, I had nine or 10 calls about clerical errors and inconsistent marking.
"It is early days, but a lot of schools say level 5 children are coming back as level 4. The early indications are that it is like two years ago."
In 2009, 50,000 test papers were returned - 3,000 more than in 2008, when the system descended into chaos.
The thresholds, which determine how many marks are needed for each level, have not yet been published. But these change very little from year to year, and some heads are concerned that the marking itself - regardless of the level awarded - is not consistent.
Adrian Hayes, head of Our Lady Immaculate RC Primary in Chelmsford, said: "It does seem like a repeat of the year before last, perhaps not as extreme in our case.
"But I have two children who have got identical marks and yet the difference between their two papers is like chalk and cheese.
"Once again we can see gaping holes in the marking process.
"This experience highlights how urgent it is that teacher assessment is used for marking writing."
The Bew review of KS2 Sats, published last week, recommended that the writing test is dropped in its current form and replaced by teacher assessment.
It also proposed the development of another test to assess spelling, punctuation, grammar and vocabulary, but said a child's overall writing mark should be largely made up of teacher assessment rather than test scores.
But this makes no difference to this year's marking.
On The TES's online primary forum, Cassandra wrote: "We received our English papers today and to say we are horrified would be an understatement... I am looking at a paper from one of our SEN pupils alongside one of our 'high fives'. There is no comparison in terms of quality, yet both were awarded the same marks. Words fail me... again."