Big Cat band 11 are approximately national curriculum level three books.
The national expectation is for an average year three child to read at level three, but schemes are not age related as such.
Some children will read above and some below this level at age 7 - 8.
Matching your child to the correct level for them is the most important part. A child is at the correct readability level if they are making one mistake in every ten words. More than this and it is too challenging. Also their ability to comprehend the book needs to be assessed.
A child also needs the confidence to self correct when they make a mistake by...
looking at the picture - predicting what it could be... (graphic)
using the sounds/phonemes in the word...(phonics)
making sense of the word by re reading the sentence and slotting in a word which fits grammatically....(semantics)
a enough knowledge of the english language to be able to predict sentence structure and slot in a word that makes sense. (syntax)
Hope this is helpful. Please will an expert come along and add/double check this information. Thanks.