Attentional control is the ability to maintain a goal and goal-relevant information in the face of distraction. Recent research has shown a difficulty of establishing attentional control as a factor explaining shared variance across tasks. This difficulty may stem from two sources of diversity. First, there is diversity in the design of typical attentional-control tasks. Second, there is diversity in the attentional-control processes. For example, proactive control (i.e., goal maintenance) and reactive control (i.e., goal reactivation) have not yet been disentangled. Our goal was to control these sources of diversity by using one task, the AX-CPT, in which we measured proactive and reactive control separately. Thus, our participants (N = 421) were asked to press a target key if the letter A was followed by the letter X and a non-target key for all other letter sequences. In addition to letters, we used words, dots, pictures, and matrices as materials. For each material, we calculated several attentional-control indices: d' proactive (= d' context), d' reactive, proactive behavioral index (PBI), BX interference, and A-cue bias. Preliminary results indicated good reliability for two proactive indices (d' proactive, PBI) and one reactive index (d' reactive) across materials (splithalf rs > .65). In contrast to the predictions, structural equation modeling showed a high latent correlation between d' proactive and d' reactive (r = .86) and a weak latent correlation between PBI and d' proactive (r = .30). These results question the validity of the attentional-control indices assessed with the AX-CPT.