Keep preschool writing activities relaxed and fun. Don't expect or require perfection. Learning to write is a fun process that will give your preschooler a boost in confidence and solid foundation for future studies.
If your third grader needs help with math, there are many useful tools that can downloaded directly from the computer. Math is a subject that is best taught with visual aids, making the lessons more tangible for students.
Many online math games are designed purely for entertainment and won't do much in terms of teaching your child. While these games can be fun and engaging for third graders, you want to choose games that will practice the skills being taught in school.
Textbooks, instruction manuals, and lesson plans are the basic foundation for any homeschooling program. Homeschooling does not have to be limited to the parents understanding of the material that the student is learning. Home school information and education should instead be based on the student's individual learning style and the materials that must be taught based on the students grade level and educational needs.