My dd has been attending a "mommy and me" type class once a week at a Montessori school. Parents are required to stay, so no problem there. I think just follow your gut, your heart, and that little voice inside ! You and your child will know when he/she are ready to start the "leave alone at school phase". I so far plan to start at age 3. Part of my reason is the Montessori theory was initially geared for the ages of 3-6 anyway. Also a big issue for my husband is that dd must be "talking" enough so that we understand what she is saying, and can "report" aobut school and anything that happens/happened. See if your school offers a class like that, also many do let you become the "class mom". Lastly if after a week of trying to get your little one to "go" to school with out you, and they are still have a very difficult transition, I would say it was too soon. Don't worry two is still very early to start "real school", it tends to be more of "daycare" at that point it seems anyway.
Now having said that, if you want to or need to get your little one in school now, try other opportunities of leaving your little one. Start with playdates with a trusted friend. Also try maybe half day of school versus a whole day.