My kids are now grown, but when they were younger we supplemented a lot. We are in MCPS which had a terrible curriculum (they're
finally acknowledging that it was deficient and are replacing it.)
If I felt there was a gap in their education, I would make sure we worked on that area so they had the foundation they needed. I tried to make it as fun as possible.
Additionally, we supplemented a lot according to their interests to enrich their education.
There were very few workbooks involved. Moreover, aside from the two cases of teaching children how to read and assigned reading of specific material, I don't think reading should be mandated. I hate the common practice today of requiring kids to read for a set period of time daily. I can think of no faster way to make somebody hate an intrinsically enjoyable activity than to force them to do it.
Some of the things we did to supplement generally:
Hoagies is a website that has links for enrichment for any subject a child might be interested in
https://www.hoagiesgifted.org/links.htm
LANGUAGE ARTS
Frequent trips to the library
Reading together (into high school)
Mad-libs
Word Games (Rhyming, Alphabet)
Schoolhouse Rock (I remembered it fondly from my childhood, but they weren't impressed)
PBS shows (Between the Lions and Ghostwriter - I think these may be off the air now)
Shakespeare's Birthday Celebration at the Folger theater
https://www.folger.edu/events/shakespeares-birthday-2019
Library Programs
MATH
Games of all types (Sleeping Queens is great for simple addition, Set is good for patterns), but just about every game is good in some way for math (keeping score, counting moves, geometrical and logical thinking, etc.)
Playing with coins (in our house once they learned to count money, they got a weekly allowance of $1.00 - in change, which they had to count before they could keep it.)
Cooking
Cyberchase on PBS
Measuring things (tape measure, ruler, balance scale)
Got an analog wall clock and wristwatch that clearly indicated minutes
https://www.amazon.com/s?k=educational+wall+clocks+for+kids&crid=C0A727M1WLH8&sprefix=educational+wall+clock&ref=nb_sb_ss_i_1_22
Buzz (a word game where you set a math rule and then count buzzing out the appropriate numbers - ex. numbers with 2 and multiples of 3 - 1, buzz, buzz, 4, 5, buzz, 7, . . . , 17, buzz, 19, (20) buzz, buzz, . . . , (29) buzz, (30) buzz, 31, buzz) This game can be adjusted for mathematical ability from very easy to very complex).
Zoombinis computer game (outstanding logic puzzles)
Math enrichment books like the Sir Cumference series, Sideways Math by Louis Sachar, and Theoni Pappas books. These books cover a broad range and some are more advanced than others.)
Computer games to practice math facts (lots of these, don't know that one is intrinsically better than the others)
Origami and crafts in general
National Library of Virtual Manipulatives
http://nlvm.usu.edu
There's a math festival (I never went because I didn't find out about it until my kids were too busy - I think it's every other year, including 2019)
http://www.nationalmathfestival.org
SOCIAL STUDIES
Smithsonian Folklife Festival
Museums
Williamsburg
Mount Vernon
Monticello
Montgomery County Heritage Days
https://www.heritagemontgomery.org/events/heritage-days/
PBS shows like Postcards from Buster and Fetch! With Ruff Ruffman (these may have gone off the air)
Maryland Renaissance Festival (great fun, but be aware that they only have portapotties)
https://www.rennfest.com
Sakura Matsuri cherry blossom festival
http://www.sakuramatsuri.org
Great Falls (Maryland side - canal boats, nice visitor center, beware of Billy Goat Trail)
SCIENCE
Museums/zoo/aquarium
Butterflies at Brookside Gardens
https://www.montgomeryparks.org/parks-and-trails/brookside-gardens/wings-fancy-live-butterfly-caterpillar-exhibit/
Magic School Bus (picture books, chapter books, TV show)
Hands on Science (a school based extracurricular class)
PBS shows (animal shows, Design Squad - off the air, NOVA)
The Incredible Machine computer game
Great Falls (see above)
Nature Centers
There's are annual science festivals (I never made it to these). Here are 2:
https://usasciencefestival.org
http://rockvillesciencecenter.org/rockville-science-day/
COMPUTERS
a typing tutor program (again, I don't know that the specific one matters)
Scratch programming language
MISCELLANEOUS
Brainpop - primarily a paid website, but they have some free topics. We just did the free topics.
https://www.brainpop.com
Free Rice
http://freerice.com/category
Artscape
http://www.artscape.org