Stay away from merging or splitting cells on the table. It is better to create two separate tables rather than merge a row in the middle of one large table indicating a new section. Merging and splitting cells can cause a user of assistive technology to get "lost" inside a table because it doesn't progress as expected.

In Microsoft Word make sure the Header Row box is checked in the Table Tools Design Tab. You must click on your table for the Design Tab to appear.

After clicking on your table, select Repeat Header Rows in the Layout Tab of Table Tools. This will ensure that if the table spans more than one page, the header row will be repeated. Always turn on Repeat Header Rows, even if the table is small and isn't currently spreading across two pages.

To add a caption, or alt text, to your table, right-click on the table and select Table Properties.

When the Table Properties box pops up, select the Alt Text Tab.

Fill in the Title and Description fields for your table. The data from the table does not need to be included in the table caption.

Click OK.