They use a theory in which lift is due to circulation of air about the wing. Notice that this is a statement about the relationship between the change in speed of a fluid parcel and the change in its pressure. Measurements made by attaching pressure sensors to the top and bottom of a wing show that the pressure is reduced at the top of the wing and that the pressure either remains at atmospheric pressure, or is above atmospheric pressure, on the bottom of the wing depending on the angle of the wing with respect to the direction of motion of the wing through the air, the angle of attack. See the Bernoulli Bottle exploration. Here is a case study using Bernoulli's equation.
Air flows over an airplane wing that is convex on the top and flat below.
The flat bottom of the wing is parallel to the velocity of the airplane. The air a great distance in front of the airplane is at atmospheric pressure. The air speeds up as it flows over the top of the wing. The same amount of air must flow through every cross sectional area so when the air flows through a smaller area over the top of the wing it must speed up. When the air in front of the wing speeds up as it passes over the wing its pressure must drop.