Best app to teach/improve sight reading?

[NaturWilde]

As in title! Starting piano grade exams and this would really help! TIA!

I would be interested, too.

Rather than 'aps' I would suggest the appropriate ABRSM books, for Theory and Sight Reading:

shop.abrsm.org/shop/dept/Piano/100007

In Sight Reading I always advise NOT to worry too much about the names of notes, but get your fingers to recognise where they need to be, straight from the stave. ANY music of roughly the appropriate difficulty can be used to reading practice, so charity shop or car boot music sheets can be used. Practice is the important thing - it doesn't really matter what sort of music it is!

(Is this for a child, or a parent? A younger child might get discouraged if the score is not quite in the format they are used to, but an adult should be more able to cope with that.)

Also, this site has information that might be of use:

www.8notes.com/piano/