Math Wizard grade 4 for iPad is one of the best apps for iPad for grade 4 students.
Math Wizard iPad app for grade 4 studentss has in-depth coverage of topics of grade 4 Math skills
The math app covers modules/topics as below:

1) Numbers and counting
a) Counting up to Ten Thousands
b) Write number to words
c) Roman Numerals
d) Identify even or odd number

2) Count using Abacus
a) Thousand, hundreds,Tens and ones

3) Addition for grade 4 kids on iPad
a) Add Three 3 digit numbers
b) Four digit number Addition

4) Subtraction for grade 4
a) Four digit Subtraction

5) Multiplication
a) Four digit multiplication
b) Two digit multiplication

6) Division for Grade 4

a) Division of 3 digit number
b) Division of complete number

7) Algebra
a) Write variable expression

8) Graph
a) Points on coordinate plane
b) Creation of line graph

9) Geometry
a) Area of Square and Area of Rectangle
b) Diameter of Circle
c) Circumference Of Circle

10) Fraction
a) Addition of 3 fraction numbers
b) Subtraction of fractions