Tides:
Activities for the Classroom
This activity published by the Massachusetts Marine Educators involves using data to graph the cycle of the tides. It is somewhat advanced for 5th grade students but could be modified. Texas educators may want to substitute the data provided from Boston Harbor with data from the Texas gulf, but should be aware that the patterns of tides in the Gulf are more complex and not as symmetrical as those on the East coast. http://www.massmarineeducators.org/curriculum/tides.shtml
Eyes on the Sky, Feet on the Ground has a similar activity in which students use data from newspapers to investigate tides: http://hea-www.harvard.edu/ECT/the_book/Chap6/Chapter6.html#t
Data from Texas tides can be found here: http://tidesandcurrents.noaa.gov/station_retrieve.shtml?type=Tide+Data