Enchanted Learning provides its "List o' Common Contractions," as well as many practice worksheets. Have Fun Teaching offers a variety of worksheets pertaining to contractions, while E Reading Worksheets has a few contraction worksheets available in RTF and/or PDF format. Most of these worksheets are free to download.
Contractions are two words in which a letter or letters are removed and replaced by an apostrophe. When writing, using both words is always considered grammatically correct. However, contractions are used in informal writing, when writing dialogue, narrative, or in advertising and slogans. Because contractions are considered informal, they are best used in casual conversations