The day tours from San Pedro to Tikal involve flying from San Pedro to Belize City and then flying from Belize City to Flores, the airport closest to Tikal. Both Maya Island and Tropic Air do this trip.
From the San Ignacio area, you'd do the trip overland by van (it's about 2 hours to Tikal from San Ignacio).
Be aware that there is a major crime wave going on now in the Peten.
Belize First Magazine http://www.belizefirst.com/