We purchased Achieve Math and Science grades 1-3 for my two children, 5 and 6 years old. We purchased Reader Rabbit 1st grade at the same time. My children choose to use the Achieve software -- Reader Rabbit is almost untouched.
The activities progress in difficulty for each user from level A to level Z. Each user moves through the levels automatically. Level A is very easy with things like counting and sorting by color, identifying shapes. These beginning level activities were suitable for my 5 year old, and might be suitable for a 4 year old, but they were too easy for my 6 year old. However, just change the level manually, and the activities are challenging -- my 6 year old started with the intermediate activities and finds the activities challenging. Neither child wants to stop playing.
The activities are obviously educational. Fractions, sorting by multiple characteristics, adding, subtraction, etc. There is very little downtime like with most other kids software. It is just one activity after another. Rewards are not long winded. There is some variety within each type of activity to make it interesting.
So, I would disagree with many of the low reviews given by other reviewers. That said, I would not recommend this software if you're child is already in grade 3 -- most of the activities would be too easy.