The first is Scott Foremen Reading which offers pdf workbooks from Grade 1 to 6. These are nice looking workbooks but they're in colour and so expensive to print. When you download and click print, if you want to reduce the cost, you can go into 'preferences' or 'properties' and change to a quick or draft print and choose to print colour pictures as black and white.
The second is English Banana.
The book is divided into four parts and is graded in difficulty, so that it begins with some basic stuff and builds up to more challenging grammar activities. It features a selection of Essential English worksheets which provide practice for crucial basic areas of knowledge for learners at Entry Level, like using numbers, writing the alphabet, spelling days and months correctly, and so on.
It's not organized by grade and seems to be targeted towards ESL teachers but looks like a great resource for teaching grammar as well. All downloads are again in pdf.