The British Council's Learn English Kids site features a new section devoted to grammar for lower level students, those at A1 (Básico 1) and A2 (Básico 2) levels. Originally, the contents are designed for children, but the material can be used by learners of all ages at an elementary level.
This is the way The British Council introduces the section on its webpage:
"Do you want to practise your English grammar? Watch the grammar videos, play the grammar games, print the grammar worksheets, write to us in the grammar quiz section and then test yourself with our downloadable grammar tests. Don't forget you can always print the grammar reference cards to help you."
As you can see from the screenshot above, there are four parts in the section. I found the grammar videos and grammar tests the most interesting ones for learners.
In the grammar videos you will find one-minute videos with explanations on a number of grammar topics: countable/uncountable nouns; future with will; present simple vs simple continuous; comparatives and superlatives; how to use prepositions of place.
In the grammar tests, you will find explanations of grammar topics with lots of examples (adjectives, past and present of to be, possessives, pronouns, demonstratives, like/don't like, modals, have got) and tests or activities for you to download together with a "reference card", which is a fast and effective way of revising and consolidating how to use a specific grammar point. You will need to register to be able to download this stuff, but it is free and you gain instant access.