Free English grammar and language resources from UCL. For CPD/INSET: bit.ly/1L78lbs and bit.ly/2jSFKCp Tweets by Prof. Bas Aarts & Ian Cushing.
You've put your finger on a very difficult issue. Not easy to solve at all.
You need to keep the two issues apart: the value of teaching grammar to young children, and testing.
But how do you decide what is "too abstract" and what is not? For maths they need to know e.g. addition, subtraction, fractions, mass, weight, 2D and 3D shapes, place value, negative numbers, etc. All of these are highly abstract, yet no one complains about that.
But is anecdotal evidence good enough? We need solid evidence. Research by Huw Bell at Manchester Metropolitan University has shown that pupils enjoy learning about grammar.
Fourthly, studying grammar makes learning foreign languages easier. And finally, learning about grammar can improve students’ critical reading and writing skills.
Secondly, learning about grammar can help students enjoy using language in both spoken & written form. Thirdly, because the study of grammar involves studying structure, students will acquire important key analytical skills which will be very valuable wherever their futures lie.
Learning about language offers many advantages: First of all, grammar is part of the language that we all use to communicate with each other, and to have some knowledge of how communication works should be part of our general knowledge.