E.T. follows a linear structure. There are no flashbacks or flash-forwards, no crazy dream sequences or red herrings; it's just a straightforward story. Boy meets alien. Alien teaches boy about friendship. Alien goes home. Boy is forever changed.
Okay, so it's not really that simple, but as a linear narrative, the events unfold in a sturdy chronological order. The only real diversions from Elliott's and E.T.'s storyline include cuts to the encroaching federal agents, but even those happen within the overall story's tidy timeline.