What I would do is get a Kaplan or Steck Vaughn book from your library. (I’ll link those at the end) As long as the publication date is after 2014, you are good. The only difference is that they lowered the score from 150 to 145 and they did away with the Science essay. The Kaplan book is large, like over 1,000 pages large, but has everything that you will possibly need to know for all four tests. They also contain practice tests that can give you a general idea of what you are still missing. I say possibly because not all tests are the same (content wise) or some minute part may change from test to test. For that, just follow this sub and you could get a pretty good idea of what maybe on it.
Website wise, I suggest Kahn Academy. It’s free and has videos and other tutorials for what you may not understand. Also, this sub is great for posting a question, especially math, and getting a pretty doll good answer. I do a lot of the answering for math fairly regularly. (I will show everything if wanted. By everything I mean 1+1=2)
I don't know of any online classes, but you might consider studying on your own. (That's what I did when I wrote the GED exam decades ago.) This particular book will have all of the study material you'll need:
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I recommend this book. If you study it, you’ll pass it. The Science & Social studies is reading comprehension. Same with language arts. I studied a bit more for math.
GED Test Prep Plus 2020: 2 Practice Tests + Proven Strategies + Online (Kaplan Test Prep) https://www.amazon.com/dp/1506258662/ref=cm_sw_r_cp_api_i_ONXNFb9Q8VCQN
I recommend this book. If you study it, you’ll pass it. The Science & Social studies is reading comprehension. Same with language arts. I studied a bit more for math.
GED Test Prep Plus 2020: 2 Practice Tests + Proven Strategies + Online (Kaplan Test Prep) https://www.amazon.com/dp/1506258662/ref=cm_sw_r_cp_api_i_ONXNFb9Q8VCQN
The Kaplan GED Test Prep Plus book is hands down THE best book for you, in my opinion. Very thorough, very extensive, and very quick to finish overall. You can buy it on amazon! It’s cheap for everything it offers. GED
I have less experience with the HiSET than GED. Most of the large all in one study guides are a good overview, but will not give a lot of practice. I think these Steck-Vaughn books are good. There is a student book and a separate workbook. They offer challenging problems, but not a lot in the way of explanation. You good look up topics on Khan Academy to get some relevant explanation. https://www.amazon.com/Steck-Vaughn-GED-Preparation-Mathematical-Reasoning/dp/0544274245/ref=sr_1_3?crid=FQTNN9H2XFVV&keywords=ged+steck+vaughn+math&qid=1571753084&sprefix=ged+steck%2Caps%2C202&sr=8-3
I passed the TASC Test and I used Kaplan's 2017-2018 TASC Study Guide prior to taking the exam.
Link: https://www.amazon.com/Strategies-Practice-Review-2017-2018-Tests/dp/1625233000
Math and Science were my two biggest worries as well but it was a lot easier than I expected. There were some nerves but it's good to have SOME as my therapist told me (I have anxiety).
If you're self-studying, you can get yourself a book like this one to help you. Several reviews by people who bought it said it's enough to pass the GED if you study consistently, so you can save yourself the money of enrolling somewhere.
Donate plasma, you will get more than enough to pay for the test in 2 weeks. The hiset is only 78. Just make sure you prep for it, a good resource unless your area has classes is the prep book you can find on Amazon -The Official Guide to the HiSET Exam, Second Edition https://www.amazon.com/dp/1259640795/ref=cm_sw_r_cp_api_lTvGybZA52392 Donate plasma, order the book, study and keep donating to save for the exam and when you can score >12 on the practice tests, take the real test. But look into those classes first, they may be required (they are usually free).
https://www.amazon.com/McGraw-Hill-Education-Preparation-GED-Test/dp/0071847200
Weighted averages, graphs, foil, finding out if something is a function or not, equation word problems, inequality word problems, geometry word problems, mean, median, mode, range, finding the slope of a graph, finding the equation of a graph, quadratic equations, simplifying equations. There's more but I took my math two months ago.
Also use OpenWindowLearning on YouTube.
Really, really easy. Pick up a practice book with practice tests if you need a confidence boost.