Future relationships - Next to his outward appearance, your child's use of grammar gives others the quickest impression of his abilities and personality. People form judgments based on the way others communicate. Good grammar makes them appear more intelligent and thoughtful, while poor grammar makes them look careless and uneducated.
Future educational opportunities - College scholarships based on ACT and SAT scores are at risk for a homeschool child who fails to use grammar correctly. The optional essay section on these tests, which is quickly becoming a requirement for entrance into most colleges, will make or break your child's final test scores. Scholarships are often awarded on the basis of these test scores, and your child's poor grammar could prevent him from receiving scholarship money that might help him attend the college of his choice.
Future career opportunities - Competition in the work force is tough. Poor grammar in cover letters, résumés, and applications is a sure-fire way to see your child lose an employment opportunity. Career advancement possibilities are also killed quickly by sloppy logic, misspelled words, and disorganized thoughts in emails and other business correspondence.
Companies are also not interested in your child's generation of high-tech Internet English. Knowing how to write a properly constructed sentence without abbreviations or text messaging jargon is a highly sought after skill by employers. The business world knows that potential customers and clients are lost by employees who fail to use proper grammar because they portray the company as less than polished and professional.
Future Christian witness - Possibly the greatest reason for learning proper grammar is to effectively communicate the love of Christ. Without a thorough understanding of the eight parts of speech and other grammar rules, your child will be unable to verbalize or write a clear presentation of the Gospel. God may want to use your child to spread the Gospel, but without good grammar skills, he will be limited in communicating God's truths clearly. "So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air" (1 Corinthians 14:9).
Good grammar isn't a thing of the past. Like learning to eat vegetables, your children may groan as you teach it to them, but someday they'll thank you for making them turn off their cell phone and teaching them how to communicate in real English.