Train from Naples to Pompeii

We took the Circumvesiviana. It's not fancy, but was absolutely fine. Just make sure to get on the train that stops at Pompeii Scavi. One of them only goes to the modern city of Pompei. My recollection is they use the same track and alternate.

I've been hearing about the Campania Express which I don't know a thing about. I did hear that the trains are less frequent.

It’s the local circumvesuviana train (downstairs at Naples train station.) We have taken it numerous times and in general I’m not a fan, especially embarking in Naples. It is often very crowded with people standing and packed in tightly with roaming musicians. I think if you can avoid any typical commuting times, including before and after school, it might not be as bad. We once took it from Sorrento to Pompeii and it was almost empty.

Here's a link to the Circumvesuviana train schedule. https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule
If you'll be arriving from somewhere else, you'll get off at Naopli Centrale and go down one level and then follow a long hallway past the Napoli subway gates and keep going until you think you must have gone too far, go a bit further and there it is. There is a ticket window to buy tickets. Get on the train heading toward Sorrento and get off at Pompeii Scavi.

It's a commuter train so you don't buy tickets in advance.

There are three trains you can take from Naples to Pompeii: the Circumvesuviana, the Campania Express, or the less frequently taken Trenitalia Metropolitana. The first two will drop you directly at the site of the ruins. The Trenitalia train connects Naples and Salerno but stops in the modern town of Pompei at a station further away from the ruins from which you can either ride a shuttle bus or walk.

The Campania Express is meant for tourists; it offers air-conditioning and (in theory) assigned seating and slightly more luggage storage. It uses the same track as the Circumvesuviana, but only runs 4 times per day as opposed to 2 times per hour. It is also more expensive at 15 euro one way vs. 2.90 euro on the regular Circumvesuviana. There are mixed reviews on whether the Campania Express is worth the extra money. I would recommend searching the travel forum about people's experiences with the trains to see which is right for you.

Sources: Online research and RS Italy Guidebook pg. 1008

I have also heard recommendations for a bus, which is direct. You might compare that as well.

There are mixed reviews on whether the Campania Express is worth the extra money.

If the train actually took less time, like the "express" implies, like 30 minutes, then it would be worth the price...but the "slow" Circumvesuvia take the same 1 hour 10 minutes that the Campania Express does. (OK,OK, the express takes 1 hour 9 minutes).

If anything the express version was meant to improve the "image" over the Circumvesuvia, keep the locals and teens off, gain a few more bucks from the tourists.