It marks further progress at the Essex comprehensive, which was upgraded by Ofsted this year from a school requiring improvement to good.
Mr Slater added: "We've focused on the core skills of numeracy and literacy."
He singled out results in Jewish studies, where 85 per cent of students received an A* to C pass. While two-thirds of the school's population is non-Jewish, all children take Judaism for GCSE. "To get that result is unbelievable," he said.
Top KKS performers Zach Igielman and Jack Palmer collected 11 A*s apiece, while Sarah Lewis bagged 9A*s and 2As.
Nationally, A*to C passes dropped by 2.1 per cent this year, with A*to A passes down by 0.7 per cent to 20.5 per cent. The fall has been attributed to a new rule that children who failed maths or English last year had to retake them, as well as a switch to more traditional academic subjects.
Teachers at JFS could also reflect on a job well done as 83 per cent of this year's students gained at least five A*to C including English and maths - compared to 77 per cent last year. Results in English and maths were the best for five years.
Headteacher Simon Appleman said the school was "particularly pleased" with the returns in Ivrit, where 79 per cent gained an A or above: drama, 86 per cent; religious studies 69 per cent. In classics and astronomy, which are taken as extra-curricular subjects, more than 70 per cent achieved an A or better.
Segev Gonen Cohen topped the school's roll of honour with 11 A*s and an A, closely followed by David Launer, Savanna Leboff, Ava Sharpe and Ze'ev Shirazi, each with 11 A*s; Eva Jacobs and Reef Ronel, 10A*s and an A; Adam Bernstein, 9A*s and 3As; and Benjamin Kershaw and Benjamin Waldman 9A*s and 2As.
While just under 21 per cent of passes nationally are A or A*, the figure for most Jewish schools is well above: 53 per cent for Hasmonean High School, around 50 per cent for King David Manchester and JFS, 45 per cent for Yavneh College in Hertfordshire and 39 per cent for JCoSS.
At KDM, nearly a third of pupils, 39, gained eight or more A or A*s. Overall, 96 per cent of pupils achieved at least five GCSEs from A* to C including English and maths.
Joshua Rowe, King David's chairman, said the trends have been "virtually the same for 15 years, they are remarkably consistent".
Alexander Demby and Daniel Moss each had 11 A*s and an A, while Hadassah Black achieved 9A*s and 3As and Sammy Pine 9A*s and 2As.
Mr Rowe was also gratified by results for modern and classical Hebrew which are taken a year early. "It's very encouraging," he said.
At Hasmonean High School, 79 per cent achieved at least five A* to C including English and maths; and 61 per cent attained the English Baccalaureate level, a suite of subjects which include geography or history, a modern language and two sciences.
For the sixth year running, more than half the grades were at A or above.
Natasha Rosenberg-Whyte and Natan Maurer each garnered 11 A*s and an A. Nathan said, "I'm extremely grateful to all my teachers, I couldn't have achieved it without their support."
Andrew McClusky, Hasmonean's executive head, said it was "wonderful to see both our brightest students and those who find academic study more challenging all achieving outstanding results".
Five students at JCoSS achieved A^s, a distinction higher than an A* for further maths. Over 79 per cent of the cross-communal school's second GCSE cohort gained at least five A*to C passes including English and maths. JCoSS head Patrick Moriarty said the results "confirm our place on the map of high-performing schools, and show the strength in depth that comes from the hard work and dedication of our staff and students alike".
Jack Margolis earned 12 A*s, an A^ and an A; Josh Cowan 12 A*s and an A^; Aviv Silver 11 A*s and an A^; Adam Gould 10 A*s and an A^; Daniel Dolan 10 A*s and 2As; Adam Aradi Posylkin 8 A*s, an A^ and 4As; Zachary Levenson and Orli Vogt-Vincent 9A*s and 3As; Joe Rogove 9A*s and 2As.
At Immanuel College, 96 per cent of pupils at the Bushey school gained at least five GCSEs from A* to C including English and maths and 55 per cent the EBacc. It was the college's second highest EBacc figure. Students also produced their highest average points score per subject at 50.8 (an A is equivalent to 52 points, B 46).
Its furthest mathematicians got their sums right with a record eight gaining an A^.
Immanuel's GCSE champions were Jemima Attar 11A*s; Alexander Root 9A*s and an A^, and Gemma Black 9 A*s.
Yavneh head Spencer Lewis said its results were "a source of great pride for our entire school community" as more than 82 per cent achieved at least five A*to Cs including English and maths.
Leading the way were Nina Freedman, Zac Garcia and Erin Wacks, each with 9 A*s and an A.
The strictly Orthodox Yesodey Hatorah Girls' High School in Stamford Hill enjoyed its best results for some years, said its principal Rabbi Avrohom Pinter, with 84 per cent achieving A*to C including English and maths.
At the Grammar School at Leeds, Ilana Pearce was on top form with a haul of 10 A*s.
An Independent table of leading comprehensives based on A*-C passes including English and maths listed King David Manchester at five: JFS 34; King David High Liverpool, 44: Yavneh 45: and JCoSS 67.
