Dyscalculia is associated with difficulties in math. Often times a student with Dyscalculia will get confused with word problems in math, and often times are unable to see patterns well. They also have difficulty in understanding things such as days or weeks on a calendar. Some accommodations for Dyscalculia include using picture for word problems, the use of scratch paper for difficult problems, and color coding work.
Dysgraphia is difficulty in writing. Often times the writing of a student with Dysgraphia is near illegible. There is often large spaces between letters and words. The position of the student's body and wrist are often strange and warped. Words can also be unfinished, and the student cannot multitask writing and thinking/processing at the same time. Accommodations for such include using a word processor (auto correct feature) and writing aids that "fix" wrist position.
Dyslexia is difficulty in reading. Dyslexia is often associated with the previous two SLD, as having dyslexia can cause difficulties in writing and math as well. Spelling is always a difficult process for students with dyslexia. Allowing the use of technology, such as laptops, helps students with dyslexia a lot. Use of audio books are always extremely helpful to students with dyslexia.
While these may be classified as "disabilities" it by no means should be used as a crutch to keep people back. The same is true for any student with a disability, as this video shows.
[1] Gargiulo, R.M. (2006). Special education in contemporary society: An introduction to exceptionality. Belmont, CA: Thomson Wadsworth.