What is the difference between the HSPT and the ISEE?

Both tests are aprox 3 hours long and test similar content in Math, Verbal Reasoning, Quantitative Reasoning and Reading Comprehension (Math covers Arithmetic, Algebra and Geometry). The ISEE has a 30 minute essay, which the HSPT does not have. The HSPT has a Grammar, Punctuation Section, which the ISEE does not have.