Bone marrow. The inside of your bones are filled with a soft tissue called marrow. There are two types of bone marrow: red and yellow. Red bone marrow is where all new red blood cells, white blood cells, and platelets are made.
Mine is 8m x 7m (3m is 10 feet, so around 27 x 23 feet). This is normal for an Australian classroom, although there's a fair bit of variation.
Open Classroom School District (UT) District Average # of Students: 400 students: 400 students # of Teachers: n/a: n/a: Student : Teacher Ratio: n/a: n/a # of Male Students: 201 students: 201 students